Borrowing the term “Flow Architectures” from the title of James Urquhart’s recently published book, Clemens Vasters will explore the elements of event-driven and message-driven architectural approaches that are fundamental for many sophisticated, large scale business solutions. We will consider systems yielding and being driven by discrete events, systems that emit, aggregate, and act on signals derived from event streams, and we will explore required and desired coupling between elements of a system and what effect that coupling has on application architecture. We will also clean up with the misguided notion that some elements of messaging, like queues, are somehow “traditional” or “legacy”, while event streams are “modern” – they are facets of the same toolbox.